Given the following vector, $\mathbf{v}$, obtain the unit vector that aligns with the direction of $\mathbf{v}$.
$\mathbf{v}=-21\mathbf{j}$

• A. $\mathbf{j}$
• B. $-\mathbf{j}$
• C. $\frac{1}{21}\mathbf{j}$
• D. $-\frac{1}{21}\mathbf{j}$

Answer: (B)